David Ward

Fast Hands-free Writing by Gaze Direction

Here we describe a method for text entry based on inverse arithmetic coding that relies on gaze direction alone and which is faster and more accurate than using an on-screen keyboard. These benefits are derived from two innovations: the writing task is matched to the capabilities of the eye, and a language model is used to make predictable words and phrases easier to write.

Walter’s two-layer hypothesis revisited: back to the roots!

Walter (Jahrb Wiss Bot 87:750–860, 1939) proposed a two-layer hypothesis, an equilibrium explanation for coexistence of savanna trees and grasses. This hypothesis relies on vertical niche partitioning and assumed that grasses are more water-use efficient than trees and use subsurface water while trees also have access to deeper water sources. Thus, in open savannas, grasses were predicted to predominate because of their water use efficiency and access to subsurface water. This hypothesis has been a prominent part of the savanna literature since first proposed. We review the literature on Walter’s hypothesis and reconsider his original intentions. Walter intended this hypothesis to be restricted to dry savannas. In his opinion, mesic and humid savannas were controlled by biotic factors and disturbances. We surveyed the global savanna literature for records of vertical niche partitioning by grasses and trees. We find that, within the scope of Walter’s original intentions, this hypothesis works remarkably well, and in some cases is appropriate for deserts as well as for dry temperate systems and even some mesic savannas.

Minimum recruitment frequency in plants with episodic recruitment

There is concern about the lack of recruitment of Acacia trees in the Negev desert of Israel. We have developed three models to estimate the frequency of recruitment necessary for long-term population survival (i.e. positive average population growth for 1,000xa0years and <10% probability of extinction). Two models assume purely episodic recruitment based on the general notion that recruitment in arid environments is highly episodic. They differ in that the deterministic model investigates average dynamics while the stochastic model does not. Studies indicating that recruitment episodes in arid environments have been overemphasized motivated the development of the third model. This semi-stochastic model simulates a mixture of continuous and episodic recruitment. Model analysis was done analytically for the deterministic model and via running model simulations for the stochastic and semi-stochastic models. The deterministic and stochastic models predict that, on average, 2.2 and 3.7 recruitment events per century, respectively, are necessary to sustain the population. According to the semi-stochastic model, 1.6 large recruitment events per century and an annual probability of 50% that a small recruitment event occurs are needed. A consequence of purely episodic recruitment is that all recruitment episodes produce extremely large numbers of recruits (i.e. at odds with field observations), an evaluation that holds even when considering that rare events must be large. Thus, the semi-stochastic model appears to be the most realistic model. Comparing the prediction of the semi-stochastic model to field observations in the Negev desert shows that the absence of observations of extremely large recruitment events is no reason for concern. However, the almost complete absence of small recruitment events is a serious reason for concern. The lack of recruitment may be due to decreased densities of large mammalian herbivores and might be further exacerbated by possible changes in climate, both in terms of average precipitation and the temporal distribution of rain.

Artificial intelligence: Fast hands-free writing by gaze direction

Here we describe a method for text entry based on inverse arithmetic coding that relies on gaze direction alone and which is faster and more accurate than using an on-screen keyboard. These benefits are derived from two innovations: the writing task is matched to the capabilities of the eye, and a language model is used to make predictable words and phrases easier to write.

Effects of different Kalahari-desert VA mycorrhizal communities on mineral acquisition and depletion from the soil by host plants

Abstract Seedlings of Vangueria infausta, an indigenous Kalahari tree, were used as plant symbionts in a pot experiment designed to measure the effect of three local vesicular–arbuscular mycorrhizal (VAM) fungal communities on mineral acquisition and concentrations in host shoots. VAM significantly affected seedlings size. The highest level of VAM mycorrhizae occurred in soil with intermediate P concentration. Two VAM communities had the highest mycorrhizal response in their soils of origin. The presence of VAM caused a significant depletion of P from soils. VAM communities differed in their ability to promote P, Ca and N uptake. A significant interaction between VAM community and soil type—in terms of Ca and N concentration in shoots—indicates a local adaptation of the VAM species.

Session A3 Rangelands as dynamic systems — Vegetation change in rangelands

Conventional management approaches in rangelands include regulation of grazing to apply selective pressures on the plant community, application of disturbance (e.g. fire), introduction of new forage species, and reductions of undesirable species. However, semi-arid rangelands around the globe are currently experiencing novel pressures and large-scale environmental changes — from increased nitrogen deposition to altered disturbance regimes and new suites of plant species (many weedy) in regional floras. We examine how these global changes constrain (or perhaps magnify) rangeland response to management interventions. Managers must understand the synergies between deliberate and background agents of change to predict system response accurately.

Fast hands-free writing by gaze direction: Artificial intelligence

Here we describe a method for text entry based on inverse arithmetic coding that relies on gaze direction alone and which is faster and more accurate than using an on-screen keyboard. These benefits are derived from two innovations: the writing task is matched to the capabilities of the eye, and a language model is used to make predictable words and phrases easier to write.